Electrical circuitry often is provided with protection from electromagnetic interference (EMI) and radio frequency interference (RFI) emanating from or entering the system. Although EMI and RFI now are often used interchangeably, EMI has been used to connote energy occurring anywhere in the electromagnetic spectrum and RFI has been limited to interference in the radio communication band. EMI energy can be generated outside as well as inside the system. External EMI energy can interfere with the operation of electronic equipment within the system, while internal EMI energy can create "cross talk" and "noise" which can cause erroneous data transmission.
Electrical connectors are particularly prone to disruptions from EMI energy because of the numerous contact areas and openings for electrical terminals and cables, but numerous electrical connectors have been designed with shielding that is effective against EMI/RFI energy. On the other hand, it often is desirable to have a shielded cable as well as shielded connectors.
A flat flexible circuit conventionally includes an elongated flat flexible dielectric substrate having laterally spaced strips of conductors on one or both sides thereof. The conductors may be covered with a thin, flexible protective layer on one or both sides of the circuit. If protective layers are used, cutouts are formed therein to expose the underlying conductors at desired contact locations where the conductors are to engage the conductors of a complementary mating connecting device which may be a second flat flexible circuit, a printed circuit board or the terminals of a mating connector.
A wide variety of connectors have been designed over the years for terminating or interconnecting flat flexible circuits with complementary mating connecting devices. However, there has not been a cost effective system for electrically connecting flat flexible circuitry which is shielded. For instance, if it is desired to shield the flat flexible circuitry, the signal conductors typically are disposed on one side of the substrate and a ground circuit is disposed on the opposite side of the substrate. At an early time, it was known to cover the opposite side of the substrate with a layer of metal such as copper for shielding and grounding purposes. However, it has been found that such metal layers significantly decrease the flexibility of the flexible circuitry. Consequently, a conductive wire mesh or grounding grid has been used on a side of the substrate, typically on the side opposite the signal conductors, for grounding and shielding purposes. The invention is directed to providing a simple, reliable and cost effective system for terminating a shielded flat flexible circuit and solving the problems of inefficient systems heretofore available. It should be understood that the invention is not limited to systems where the signal conductors and ground conductors (or grid) are disposed on opposite sides of the flat flexible circuit substrate. Both the signal conductors and the grounding conductors can be disposed on the same side of the substrate.
It should be noted that the invention can be used in related systems, such as with controlled impedance cable or other types of cable where high speed transmissions necessitate shielding and other electrical considerations.